This invention pertains to carbon dioxide (CO.sub.2)-enhanced recovery systems for crude oil and natural gas with improved CO.sub.2 -corrosion resistant cement and to methods of providing CO.sub.2 -resistant encasement of metal tubular members in a CO.sub.2 -rich environment.
Enhanced production of crude oil or natural gas (generally referred to as hydrocarbons) from partially depleted underground deposits thereof by the injection or pressurization of the underground formation including the deposit with carbon dioxide (CO.sub.2), injected alternately or together with water, is known. Such processes are described, for example, in "Carbon Dioxide: Miscible Flooding Methods", "Effective Water Injection," SPE (June, 1975), 217, Oil and Gas Journal, Dec. 27, 1982. The CO.sub.2 corrosive attack on well cement and metal tubular goods in the injection or production wells of such systems has been identified as a significant potential problem. See for example, "Effects of Super-Critical Carbon Dioxide on Well Cements"--Onanan, Halliburton Services, SPE 12595 and "Carbon Dioxide Corrosion Resistance in Cements"--Bruckdorfer, Dowell Schlumberger, CIM 85-36-61. These publications detail the chemical mechanism of the CO.sub.2 -corrosion attack on Portland cement and secondarily on metallic members exposed to a CO.sub.2 -water environment. These corrosive factors may be adversely affected by the high pressure and high temperature often present at the depth of subterranean formations in which hydrocarbon deposits are found.
It is, therefore, a general object of the present invention to provide enhanced hydrocarbon recovery systems including means for injecting CO.sub.2 into subterranean hydrocarbon formations and including means for minimizing CO.sub.2 -corrosion attack on system components particularly including well sealing cements.